Corps: more room needed in Missouri River channel, not reservoirs, for flooding

The Corps of Engineers has released a study that suggests more room to hold flood waters is needed along the Missouri River channel, not in its upstream reservoirs.

The Missouri River Basin (courtesy; US Army Corps of Engineers)

The study evaluated how greater storage allowances in the reservoirs would have performed in historic runoff years between 1930 and 2011. The findings say more storage would not have prevented widespread damage in the 2011 flood, or the need for record releases from those reservoirs.

Northwest Division Commander Brigadier General John McMahon says it showed that additional flood control storage, alone, is not the answer.

“We’ve got to have adequate channel capacity to accommodate whatever flow we decide to.” What that means is, “generally, it’s moving the levees further back to accommodate whatever flow you want to design an improved system to.”

General McMahon says since the 1944 Flood Control Act was written, conditions on the River have changed. “The levees that were envisioned in that original authorization, some of them were never built. In other cases, they weren’t separated by the recommended distances to accommodate 100,000 cubic feet-per-second flows. In addition to that what we have is a lot of accumulation of soil deposits in the flow way and channel degradation.”

He says increasing channel capacity does not necessarily mean taking land out of farm production. “You can still farm on the wet side of the levee when it’s not flooded there, which is most of the time. And oh, by the way, there’s always what we call ‘interior drainage,’ that is land taken out of production that’s on the dry side of the levee but because of local drainage it’s flooded and it stays flooded because there’s no accommodation for draining that field through the levee. So the notion is not it’s an either/or proposition.”

The Corps says the report is not intended to be a complete analysis of impacts and is not a decision document. General McMahon says, “it begins the dialogue in the Basin to help discern what we might do in the future to reduce flood risk, to increase performance of the system and its resilience, to minimize damage due to events like we endured during 2011.”